FIG. 1 depicts a schematic diagram of a portion of a typical wireless communications system 10. The wireless communications systems 10 comprises a mobile switching center (MSC) 12 and a plurality of base stations 14-i. MSC 12 is connected to each of base stations 14-i and a public switching telephone network (PSTN) 16. Each base station 14-i includes a radio unit and antennas connected to the radio unit for providing wireless communications services to mobile telephones 18-j within an associated geographical coverage area referred to herein as a cell 20-i, and is operable to manage radio channel resources belonging to that base station 14-i. Power supplies, not shown, provide electrical power to the base stations 14-i.
The antennas are mounted on a vertical support at an altitude sufficient to provide the base station 14-i with optimum radio frequency (RF) coverage to mobile telephones 18-j within cell 20-i. The antennas may be omni-directional or directional depending on whether the cell is sectorized, i.e., divided into sectors A, B, C. Typically, cells are sectorized in order to reduce cost by decreasing the total number of base stations needed to serve mobile telephones 18-j. If a cell is sectorized, each base station 14-i will have a directional antenna for transmitting and receiving signals to and from mobile telephones 18-j within each sector. Typically, the cells are sectorized into three sectors, and the directional antennas provide approximately 120.degree. of RF coverage for each sector.
The radio unit comprises a plurality of radios for modulating, transmitting, receiving and demodulating radio signals. The radio unit is usually connected to the directional antennas by electrical connections and positioned near the base of the vertical support such that it is serviceable at ground level. In one embodiment of the prior art, the radio unit and the antennas are mounted on an adjustable platform that may be collectively positioned at varying altitudes along the vertical support. See FIG. 2, which depicts a base station 60 having three directional antennas 62-t, a radio unit 64 and a power supply 66, wherein the power supply includes a direct current power supply and means for converting alternating current to direct current.
The configuration of FIG. 2 has several advantages: first, the position of the antennas and the radio control unit may be re-positioned to a different altitude in the event of a terrain change within the cell; second, the antennas and the radio unit may be positioned to an altitude along the vertical support that makes them inaccessible to vandals; third, the antennas and the radio unit may be lowered such that they are serviceable at ground level (by lowering the adjustable platform to ground level). However, when any of the antennas and/or the radio unit need to be serviced, the base station will temporarily disrupt wireless communications services to all mobile telephones within its associated cell when the adjustable platform is lowered to ground level to be serviced. Accordingly, there exists a need for a base station that provides the advantages associated with the pr io r art base stations without the aforementioned disadvantage.